The July 2025 Mussel of the Month is Alathyria pertexta
Alathyria (Hyriidae) is a genus of four species from Australia and New Guinea.
The Australasian genus Alathyria sits at the intersection of two different themes running through freshwater mussel systematics: the non-monophyly of traditional mussel genera and the sister relationships of freshwater mussel families. Since the earliest days of freshwater mussel phylogenetics, the “prodigious polyphyly” of genera has stuck out like a sore thumb (Lydeard et al., 1999; Campbell et al., 2025). And, for even longer, the evolutionary relationships of the family Hyriidae have posed a challenge to simple classification schemes.
The problem of Alathyria non-monophyly is a relatively recent one. The current genus-group level classification of Australasian freshwater mussels was solidified by McMichael & Hiscock (1958). That work (in the ICZN Art. 8 sense, publication) was an exemplary bit of mid-20th century revisionary work (as in effort), and the genus-level classification of McMichael & Hiscock (1958) is still in use.
The PDF linked above with data exported from the MUSSEL Project Database illustrates the near perfect consistency between McMichael & Hiscock (1958), a relatively recent review by Walker et al. (2014), and the current MUSSELpdb classification: New Zealand species have been removed to their own genus, a couple other nomenclatural changes, a few new species, but otherwise the same — especially compared to other parts of the world like North America and East Asia which have seen much more genus- and species-level flux.
A decade ago, Graf et al. (2015) found that Alathyria was not monophyletic, and we wrote about it when Alathyria jacksoni was the Mussel of the Month. In those days, the mussel systematics community was a little more taxonomically conservative in that, when our cladistic analysis recovered traditional genera as non-monophyletic, we were satisfied to just point it out and leave it to someone else to do the revisionary work. The nomenclature of classification can be tedious, globe-trotting among the world’s natural history museums to examine the types and voucher specimens that form the basis of our knowledge is expensive and time consuming, and unsexy synonymies don’t get you tenure. Rather than shelling out valuable time and money for the taxonomic tune-up, we just kept driving around with the “check genus” light on.
Since 2015, the pendulum has swung the other direction. For the new generation of freshwater mussel systematists, post hoc interpretation of molecular phylogenetic tree topologies, significant (or at least sufficient) genetic distances, and diagnostic SNPs are the modern standards to recognize new species, genera, and family-group level taxa (tribes, subfamilies, etc.). As a result, in the 18 years since our first global checklist (Graf & Cummings, 2007), the number of freshwater mussel species has increased by 20% (from 840 to 1020) and genera are up by a third (161 to 214).
We would like to think that our checklists (Graf & Cummings, 2007, 2021) and the MUSSEL Project Database have contributed to the acceleration of freshwater mussel revisions. The MUSSELpdb has made it easy to find the synonymies, Genbank sequences, specimen records, conservation status assessments, phylogenetic results, and publications that form the current classification of freshwater bivalves. In the olden days, comprehensive revisionary work was largely limited to major natural history museums, with their extensive specimen collections and libraries. That is less the case nowadays, thanks to the MUSSELpdb and other, less specialized efforts like GBIF, MolluscaBase, the Biodiversity Heritage Library, etc.
Since the COI, 16S, and 28S nucleotide data were originally published by Graf et al. (2015), they have been reanalyzed in various contexts, and the results have been reasonably consistent. As can be seen on the Velesunioninae Cladomics page of the MUSSELpdb, Alathyria is not monophyletic, and neither is Velesunio. Alathyria jacksoni is the type species of Alathyria. No matter what revisions happen, if there is an Alathyria, then Alathyria jacksoni will be one of its species. But, our Mussel of the Month Alathyria pertexta has consistently been recovered as something else. Somebody should do something!
The solution for "Alathyria" pertexta itself is pretty straightforward since we don’t have to come up with another genus name for it. Quaesithyria wardi Iredale, 1943 has been treated as a junior synonym of Alathyria pertexta by everybody except Tom Iredale, and that species is the type of the genus Quaesithyria. Alathyria pertexta could simply be shifted to that genus right now and one less problem of prodigious polyphyly would be gumming up the works.
For the time being, we will keep Alathyria pertexta where it is for at least two reasons. In other situations, where we have been proactive about revising genera — for example, Alasminota and Pressodonta — subgenera had already been recognized in comprehensive revisions. Such is not the case with Alathyria. It seems like no one has given Quaesithyria a second thought since it was described. Also, we are led to believe that a new, comprehensive phylogeny is eminent from the Aussies and their collaborators. Let them deal with it! (There is a place for them to comment on the issue below!)
If you read this far to find about the sister group of the family Hyriidae, you will be disappointed. We will have to save that for another time…
Click the link to go to this post on the MUSSEL Project Web Site.
To find out more about the classification of Alathyria and other Australasian mussels, check out:
Campbell, D.C., J.M. Serb, J.E. Buhay, K.J. Roe, R.L. Minton & C. Lydeard. 2005. Phylogeny of North American amblemines (Bivalvia, Unionidae): prodigious polyphyly proves pervasive across genera. Invertebrate Biology 124(2): 131-164.
Graf, D.L. & K.S. Cummings. 2007. Review of the systematics and global diversity of freshwater mussel species (Bivalvia: Unionoida). Journal of Molluscan Studies 73: 291-314.
Graf, D.L. & K.S. Cummings. 2021. A 'big data' approach to global freshwater mussel diversity (Bivalvia: Unionoida), with an updated checklist of genera and species. Journal of Molluscan Studies 87(1): eyaa034, 36 pp.
Graf, D.L., H. Jones, A.J. Geneva, J.M. Pfeiffer & M.W. Klunzinger. 2015. Molecular phylogenetic analysis supports a Gondwanan origin of the Hyriidae (Mollusca: Bivalvia: Unionida) and the paraphyly of Australasian taxa. Molecular Phylogenetics and Evolution 85: 1-9.
Lydeard, C., R.L. Minton & J.D. Williams. 2000. Prodigious polyphyly in imperilled freshwater pearly-mussels (Bivalvia: Unionidae): a phylogenetic test of species and generic designations. [in] The Evolutionary Biology of the Bivalvia (Harper et al., eds.). Geological Society, London Special Publications 177: 145-158.
McMichael, D.F. & I.D. Hiscock. 1958. A monograph of the freshwater mussels (Mollusca: Pelecypoda) of the Australian region. Australian Journal of Marine and Freshwater Research 9(3): 372-508.
Walker, K.F., H.A. Jones & M.W. Klunzinger. 2014. Bivalves in a bottleneck: Taxonomy, phylogeography and conservation of freshwater mussels (Bivalvia: Unionoida) in Australasia. Hydrobiologia 735: 61-79.
Hi Dan! Thanks for covering the species. You might be interested in our recent paper that includes morphological descriptions of the glochidia of several Alathyria species (see Klunzinger et al. 2023). Revisions of the taxonomy are on their way with a taxonomic grant from the Australian Biological Resources Study. A group us in Australia, along with some colleagues in your region, are in the process of sequencing as we speak and with a greatly expanded dataset, we should be able to resolve taxonomic issues over the next several months. Musselp is an invaluable resource that has inspired much of our work, so thank you!